It's double tax (U.S. + EU tax) starting @ 150 EUR:
Order value 160 USD (145.45 EUR) = no import tax
Order value 170 USD (154.54 EUR) = 30.91 EUR import tax
(rate: EURUSD 1.1)
I know it's stupid and it doesn't make any sense. I think you can avoid double tax in some cases by making several orders worth 140 EUR or something if shipping rates are good